Journal of Superconductivity and Novel Magnetism最新文献

The study focuses on analyzing the critical current angular dependencies of coated conductor samples that are sliced in both longitudinal and transverse directions of the tape. It is evident that in both cases, beside the dependence on magnetic field direction there is a distinct dependence of the critical current value on the direction of the Lorentz force that acting on the vortex matter. Asymmetry of the peaks is detected in the longitudinal sample, whereas this phenomenon is notably absent in the transverse sample. This is found to consist with the prevalent ab-plane tilt around the axis that coincides with the tape direction. An interpretation of this asymmetry is proposed that naturally follows from the empirically noted duality of the critical current anisotropy with respect to both the magnetic field and the Lorentz force directions. This analysis establishes, for the first time, a direct link between the ab-plane inclination angle and pinning characteristics, marking an advance in elucidating the structure–property relationship.

Almost all the properties of cuprate high-temperature superconductors are no less mysterious than their superconductivity. From the very beginning of their study, it was noted that a two-component system of charge carriers is suitable for their description, which, however, had to be introduced phenomenologically. Recently it has been shown that ground and low-excited states of a system with strong long-range electron-phonon interaction and cuprates-like dispersion at carrier densities characteristic of cuprate superconductors are a two-liquid system of charge carriers comprising Bose-liquid of large bipolarons and Fermi-liquid of delocalized carriers. The phase diagram of such a system was demonstrated to coincide with that observed in cuprates. The temperature of the superconducting transition in them was shown to increase with the number of conducting layers in the unit cell, like in cuprates, due to the change in the spectrum of elementary excitations of the bipolaron liquid. Here we calculate temperature and doping behavior of the electronic specific heat and Hall resistance of such systems and compare it with that observed in cuprates. The low-temperature electronic specific heat obtained demonstrates giant increase at increasing doping, like that observed in cuprates at the overdoping. The increase is related with gradual decay of bipolarons at increasing temperature or doping. We also show that this decay may be responsible for the decrease in Hall resistance with increasing temperature observed in cuprates.

Josephson junctions are key elements in superconducting electronics. The most common type is the overlap (sandwich-type) junction, formed by vertically stacking two superconducting layers. In contrast, planar junctions are fabricated without overlap, at the edge of two superconducting films within a single plane. This geometric distinction has a significant impact on their physical properties. The planar geometry greatly enhances sensitivity to magnetic fields and improves impedance matching for terahertz (THz) devices. Its two-dimensional structure allows for simple and flexible electronic component design, enabling drastic miniaturization. Here I highlight recent advances in the application of planar junctions for novel technologies, including junction-on-cantilever sensors for super-resolution magnetic imaging, vortex-based memory cells, and programmable superconducting diodes. I will also discuss the general requirements, future perspectives, and key challenges in the evolving field of superconducting electronics.

The structural, optical, and magnetic properties of TiO₂ nanoparticles were systematically investigated to explore the origin of room-temperature weak ferromagnetism (RTFM). Structural analysis confirmed the presence of a tetragonal anatase phase with high crystallinity, exhibiting characteristic vibrational modes of pure TiO₂ and surface functional groups associated with Ti–O bonding. Optical studies revealed a indirect bandgap of ~ 3.24 eV, slightly higher than the reported 3.20–3.22 eV for pure anatase, along with defect-related electronic transitions. The morphology indicates uniformly distributed nanocrystallites, and the magnetic measurements demonstrate a weak ferromagnetism at room temperature, which most likely arises from intrinsic defects such as oxygen vacancies. Compared with literature, where anatase TiO₂ is typically diamagnetic and or shows the RTFM only after defect engineering, the observation of weak ferromagnetism in undoped samples highlights the intrinsic role of defects in magnetic ordering. These insights are likely to advance the understanding of defect-driven magnetism and suggest promising applications of anatase TiO₂ nanoparticles in optoelectronics and spintronics.

This study systematically investigates the non-equilibrium magnetic loop responses (DMHBs) of a mixed-spin (1, 7/2) Blume-Capel Ising system (BCIS) on a hexagonal lattice under an sinusoidal magnetic stimuli using the PPM framework (PPM). We explore the effects of the system parameters: exchange interaction parameters (({J}_{sigma S}) and ({J}_{SS})), temperature (T), oscillating magnetic field frequency (ω), crystal field parameter (d), and kinetic rate constants (({k}_{2})). Our findings reveal complex and varied hysteresis loop morphologies, including triple, double, and elliptical loops, for both individual sublattices (({m}^{A}) ​,({m}^{B})​) and total magnetization (({m}^{T})). We analyzed the corresponding coercive fields (CFs) and remanent magnetizations (RMs). The results demonstrate how changes in these parameters significantly influence the DMHBs, leading to characteristics indicative of both hard and soft magnetic materials. Notably, the kinetic rate constant ({k}_{2}) ​ is found to play a crucial role, analogous to wheel speed in rapid solidification processes, affecting the loop area and thus the “hardness” of the simulated magnet. While our theoretical predictions generally align with existing theoretical literature, some interesting discrepancies with experimental observations are noted. These differences may arise from practical limitations in experimental setups, such as the achievable wheel speed in melt spinning, or variations in the compositional concentrations of magnetic alloys. This research provides valuable insights into the non-equilibrium dynamics of molecular-based spin-configured molecular systems and extends the application of the PPM to complex mixed-spin systems.

The Bethe lattice (BL) sites are filled with the diatomic molecules consisting of one spin-1/2 and one spin-3/2 atoms, then they are let to interact with the nearest-neighbor (NN) molecules through bilinear exchange interactions. Additionally, they are affected by both an external field, magnetic field H, and an internal one, the crystal field D. The model is then examined in terms of the exact recursion relations (ERR) by studying the temperature fluctuations in magnetizations associated with each type of spin for various coordination numbers q=3, 4, and 6. The phase diagrams are calculated under ferromagnetic (FM) case on the D-temperature planes with zero H, i.e., spontaneous magnetizations. The effects of H on magnetizations are also displayed. The model displays several critical phenomena which may be new to this model; the existence of the first-order phase transition lines and tricritical points (TCP).

The structural, electronic, magnetic, and photocatalytic properties of the vacancy-ordered double perovskites K₂MCl₆ (M = Re, W, Ru, Os) were systematically investigated using first-principles calculations within the WC-GGA, TB-mBJ approaches. The optimized lattice constants show excellent agreement with experimental data, with deviations below 0.5%, confirming the high accuracy of the structural description. Energy–volume analyses for NM, FM, and AFM configurations demonstrate that the ferromagnetic phase is the ground state for all compounds, driven by spin polarization of the B-site d electrons. The calculated magnetic moments further support the robust FM ordering. Electronic band structures and DOS reveal mixed behavior: K₂ReCl₆ exhibits a semiconducting character, whereas K₂WCl₆, K₂RuCl₆, and K₂OsCl₆ display half-metallicity, with metallic states in one spin channel and a finite gap in the opposite one. The TB-mBJ band gaps enhance the reliability of the electronic description. Thermodynamic stability is confirmed through negative formation energies and positive cohesive energies. Band-edge positions evaluated through qualitative electronegativity trends and quantitative spin-polarized electronic calculations indicate favorable alignment for photocatalytic reactions, suggesting potential for water splitting and CO₂ reduction. The combined structural, magnetic, and electronic stability highlights K₂MCl₆ compounds as promising candidates for photocatalysis and spintronic applications.

In this paper, flower-like nickel oxide (NiO) nanostructures were synthesized successfully by a green and cost-effective hydrothermal method. The approach therefore constitutes a hydrothermal-like green process using ordinary laboratory glassware instead of conventional autoclaves. The structural characterization confirmed the existence of a cubic phase of NiO with crystallite average sizes ranging from 41.80 to 89.07 nm, depending on the annealing temperature. Morphological analysis by SEM revealed well-aligned nanoflowers at 300–400 °C, while high-temperature heating led to the deterioration of the hierarchical structure. Raman spectra confirmed the vibrational modes of NiO, and magnetic measurements revealed weak ferromagnetic behavior that was consistent with superparamagnetic properties. These findings are indicative of the potential of flower-like NiO for application in environmental remediation and gas sensing devices.

Cobalt-substituted barium hexaferrite (BaCo₂Fe₁₆O₂₇, x = 0) and its cobalt-nickel co-substituted counterparts (BaCo_1.6Ni_0.4Fe₁₆O₂₇, x = 0.4; and BaCo_1.4Ni_0.6Fe₁₆O₂₇, x = 0.6) were successfully synthesized via the sol-gel auto-combustion method. This synthesis route allowed for homogeneous mixing and yielded phase-pure hexaferrite structures with controlled morphology. Structural analysis confirmed the formation of the W-type hexaferrite phase, while the incorporation of Co²⁺ and Ni²⁺ ions resulted in notable changes in lattice parameters and crystallite size. The microstructure displays notable grain size heterogeneity, densely packed grains, indicative of partial sintering and strong interparticle interactions. FTIR spectroscopy showed the Fe–O stretching vibrations associated with tetrahedral sites remained largely unaffected by variations in nickel and cobalt substituting concentrations. In contrast, the Fe–O stretching modes at octahedral sites exhibited a slight but discernible redshift, indicating subtle modifications in the local bonding environment. UV-Vis spectroscopy demonstrated a redshift in the absorption edge and a reduction in optical bandgap with increasing Ni content, attributed to modifications in the electronic structure. Magnetic measurements revealed significant enhancement in coercivity and saturation magnetization due to the substitution effects, particularly at higher Ni concentrations. The saturation magnetization (M_s) initially decreases from 72 emu/g (x = 0.0) to 66.6 emu/g (x = 0.4) due to Fe³⁺ moment dilution by Co/Ni substitution, then recovers to 71.74 emu/g (x = 0.6) as Ni²⁺’s higher moment and improved spin alignment dominate. The magnetic anisotropy constant (K) mirrors this trend declining from 0.361 × 10⁶ erg/cm³ to 0.145 × 10⁶ erg/cm³ before rebounding to 0.339 × 10⁶ erg/cm³ indicating restored anisotropic stability via spin-orbit coupling at higher substitutions. These findings highlight the potential of Co- and Co/Ni-substituted barium hexaferrites for applications in high-frequency devices, microwave absorption, and magneto-optical systems.